A method for optimizing cross-basin water resources allocation in island areas considering flood and drought conditions

Abstract

The present invention discloses a method for optimizing the allocation of cross-basin water resources in island areas considering the encounter of flood and drought, comprising the following steps: S1, collecting and arranging the hydrological and water conservancy engineering characteristic data of the mainland and island areas, and systematically generalizing according to the geographical location and hydraulic connection of the reservoirs in the mainland and island areas; S2, constructing the multidimensional joint distribution of runoff in the mainland and island areas using the Copula function based on the system generalization result; S3, deriving the probability of encountering flood and drought in the mainland and island areas based on the multidimensional joint distribution, simulating the runoff sequence in the mainland and island areas under different encounters of flood and drought; S4, establishing a joint optimization scheduling model for complex water engineering groups in island areas, taking the runoff sequence under different encounters of flood and drought as input, and carrying out the optimization allocation of cross-basin water resources in island areas considering the encounter of flood and drought. The present invention is conducive to coordinating the joint scheduling of water diversion from the mainland and water sources on the island, reducing the cost of water supply, maximizing the reduction of the contradiction between supply and demand, and realizing the efficient use of water resources.

Description

Technical Field

[0001] The present invention belongs to the field of water resource allocation, and specifically relates to a method for optimizing the allocation of cross-basin water resources in an island area taking into account the occurrence of floods and droughts. Background Art

[0002] Compared with the continental areas at the same latitude, the islands have less precipitation, greater evaporation, and special topography, resulting in less available surface water resources. Coupled with the poor groundwater storage conditions, freshwater resources in the islands are extremely scarce. Affected by the characteristics of water resources in the islands, the water sources of the islands are usually unable to meet their own needs, so water needs to be diverted from the mainland to ensure that the water needs of the islands are met. However, diverting water from the mainland is not unlimited. When the water resources on the mainland are also in a state of shortage, water cannot be supplied to the islands. Therefore, it is very important and urgent to analyze how to achieve efficient use of water resources during the scheduling period through the optimal allocation of water resources when the islands and the mainland are in a dry state at the same time (same dry).

[0003] At home and abroad, there have been studies and analyses on the flood and drought situations of islands in various regions and river basins. However, when allocating and dispatching water resources under different flood and drought situations, the water volume data of many years or a certain frequency were used for calculation, which lost the inter-annual variation characteristics, making the dispatching scheme obtained from it less consistent with the actual situation, and to a certain extent reducing the utilization rate of water resources. In addition, there are few studies on the allocation of water resources in island areas. Some studies have failed to take into account the characteristics of island areas and the premise that they need to combine with mainland water diversion projects to meet their own water needs. For the water supply sources in the configuration, most studies focus on balancing the contradictions between users, but in fact there may be hydraulic connections between water supply sources, which will have a certain impact on the calculation of water supply guarantee rate. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention proposes a method for optimizing the allocation of cross-basin water resources in island areas taking into account the occurrence of wet and dry seasons.

[0005] To achieve the above technical problems, the technical solution of the present invention is:

[0006] A method for optimizing the allocation of water resources across river basins in an island region taking into account the occurrence of floods and droughts, comprising the following steps:

[0007] S1. Collect and organize the hydrological and hydraulic engineering characteristic data of the mainland and island regions, and systematically generalize them according to the geographical location and hydraulic connection of reservoirs in the mainland and island regions;

[0008] S2. Based on the system generalization results, the Copula function is used to construct the multidimensional joint distribution of runoff between the mainland and island regions;

[0009] S3. Based on the multidimensional joint distribution, the probability of wet and dry seasons in the continental and island regions is derived, and the runoff sequences in the continental and island regions under different wet and dry seasons are simulated;

[0010] S4. Establish a joint optimization scheduling model for complex water engineering projects in island areas, use the runoff sequences under different flood and drought conditions as input, and carry out cross-basin water resource optimization allocation in island areas taking into account flood and drought conditions.

[0011] Furthermore, the hydrological characteristic data in step S1 include runoff in the mainland and island areas, and the water conservancy project characteristic data include characteristic parameters of water plants, pumping stations, reservoirs, water pipelines and the water catchment area of ​​reservoirs.

[0012] Furthermore, in step S2, a multi-dimensional joint distribution of runoff in the continental and island regions is constructed, wherein the number of dimensions n1 in the continental region is determined according to the number of water sources, the number of dimensions n2 in the island region is determined according to the number of water plants, and the total latitude N=n1+n2.

[0013] Furthermore, in step S2, a multidimensional joint distribution of runoff between the continent and the island region is constructed based on the Copula function, and the specific steps are as follows:

[0014] S21. Based on the results of system generalization, determine the correlation between runoff in the mainland and island areas;

[0015] S22. Use known marginal distribution models to fit the marginal distribution of runoff in the mainland and island regions respectively, and select the optimal distribution based on the Akaike Information Criterion (AIC criterion), Bayesian Information Criterion (BIC criterion), root mean square error (RMSE) and hypothesis test. The marginal distribution models commonly used are Pearson III distribution (P-Ⅲ), exponential distribution (EXP), generalized extreme value distribution (GEV), normal distribution (NORM) and lognormal distribution (LOGN);

[0016] S23. Based on the preferred marginal distribution, the known Copula function model is used to fit the multidimensional joint distribution of runoff in the continental and island regions, and the optimal distribution is selected according to the AIC criterion, BIC criterion and RMSE. In the field of hydrology, the Copula function model often uses the "Gaussian", "Clayton", "Frank", "Gumbel" and "Vine" functions.

[0017] Furthermore, in step S3, the probability of encountering flood and drought in the continental and island regions is derived based on the multidimensional joint distribution, and the runoff sequence in the continental and island regions under different flood and drought encounter conditions is simulated. The specific steps are as follows:

[0018] S31. Derive the probability calculation model of wet and dry seasons in mainland and island regions based on mathematical statistics methods;

[0019] S32, based on the marginal distribution and the multidimensional joint distribution and the probability calculation model of flood and drought encounter in the continental and island regions, obtaining a variety of flood and drought encounter probability values, and analyzing the flood and drought encounter situations in the continental and island regions, including the situations where the runoff in the continental and island regions appears synchronous flood and drought and asynchronous flood and drought;

[0020] S33. Simulate runoff sequences in continental and island areas under different flood and drought conditions.

[0021] Furthermore, the simulation of runoff sequences for the mainland and island regions under different flood and drought conditions in step S33 is specifically based on the marginal distribution, finding the runoff corresponding to different flood and drought probabilities, and finding the closest runoff in the actual runoff, and using the proportional relationship between the two to fit the annual monthly runoff sequences under different encounter scenarios using the same multiple ratio method for the original runoff sequence.

[0022] Furthermore, the specific steps in step S4 are as follows:

[0023] S41. Establish and solve the joint optimization dispatching model of complex water engineering groups in island areas, take the runoff sequence under different flood and drought conditions as input, and obtain the set of optimal configuration schemes corresponding to different flood and drought conditions;

[0024] S42. Optimal selection of multi-attribute decision-making method based on subjective and objective combined weighting.

[0025] Furthermore, the specific steps of step S41 are as follows:

[0026] S411. Determine the objective function of the optimization configuration model, including: maximizing the water supply guarantee rate, maximizing the water supply economic benefit, and minimizing the water supply cost, which are:

[0027]

[0028] In the formula, x ij is the total water supply from water source i to water user j (m 3 ), I is the number of water sources, J refers to water users, WD j is the total amount of water required by water user j during the scheduling period (m 3 ), α i is the water supply order of water source i, β j is the fairness coefficient of the water user, b ij is the unit water economic benefit coefficient of water source i to water user j, C island Cost of water supply to the island (yuan), C mainland Cost of diverting water to the mainland (Yuan).

[0029] S412. Determine the constraints of the optimization configuration model, including: water balance constraint, reservoir water supply constraint, pump station flow capacity constraint, pipeline water delivery capacity constraint, island water supply and mainland water diversion constraint, user water demand constraint, and variable non-negative constraint, in order:

[0030]

[0031] In the formula, S t+1 , S t are the initial and final water storage of the reservoir in the current period (m 3 ), I t , WS t is the inflow and outflow of the reservoir in the current period (m 3 ), ET t , ST t are evaporation and leakage respectively (evaporation and leakage are neglected in this study, m 3 ), is the total inflow of the node (m 3 ), is the total outgoing traffic of the node (m 3 ), WS i The current storage capacity of water source i and the inflow flow in the current period and the water supply (outflow flow) to each water plant in the previous period are considered, and the value finally obtained by calculation is used as the water supply capacity of the reservoir in the current period (m 3 ), The amount of water in the reservoir that is supplied by pumping stations (m 3 ), The amount of water in the reservoir that is supplied by gravity, siphon, etc. (m 3 ), is the maximum pumping flow rate (m 3 ), is the maximum flow capacity of pipeline m in a unit period during the dispatch process (m 3 ), X island The total amount of water taken from the island in 12 months of the year (m 3 ), X mainland is the total amount of water diverted from the mainland (m 3 ), W island_max The upper limit of water withdrawal from the island in one year (m 3 ), W mainland_max The upper limit of water diversion from the mainland in one year (m 3 ), WD j is the total amount of water required by water user j during the scheduling period (m 3 ), αj is the lower limit of the total water volume that water user j needs to control during the scheduling period (m 3 ), x ij is the total water supply from water source i to water user j (m 3 ).

[0032] S413. According to the characteristics of the model, a suitable method is selected to solve the model. The runoff sequence under different flood and drought conditions is used as input to obtain a set of water resource allocation plans under different flood and drought conditions. The solution methods commonly used are non-dominated sorting genetic algorithm (NSGA-II algorithm), large system decomposition-dynamic programming aggregation algorithm, linear weighted method and hierarchical solution method.

[0033] Furthermore, the preferred solution of the multi-attribute decision-making method based on subjective and objective combined weighting described in step S42 comprises the following specific steps:

[0034] S421. Establish an evaluation index system taking into account economic, social and ecological benefits;

[0035] S422. Determine the subjective weight and objective weight of each indicator. The subjective weighting method often uses the Delphi method and the hierarchical analysis method; the objective weighting method often uses the principal component analysis method, the two-stage method, and the entropy weight information method. Under different situations of abundance and scarcity, the importance of each indicator is different.

[0036] S423. Use the subjective and objective combined weighting method to obtain the combined weight of each indicator as the basis for judging the importance of each indicator, and rank the various options to obtain the relatively optimal option. The subjective and objective combined weighting method often uses the additive synthesis method, the multiplicative synthesis method, the extreme difference maximization combined weighting method, and the combined weighting method based on objective correction of subjective.

[0037] The present invention adopts the above technical solution, which has the following advantages and beneficial effects:

[0038] (1) This method constructs a multidimensional joint distribution with interdependent relationships, studies the encounter probability and joint probability distribution of runoff in different regions and water inflow of different magnitudes, and realizes accurate quantitative analysis of flood and drought encounters, providing scientific and technical support for flood control and drought relief, rainwater resource utilization, and rational development of water resources in island areas.

[0039] (2) The water resource optimization allocation plan that takes into account the occurrence of floods and droughts focuses on the balance between the water supply of multiple water sources and the water demand of multiple water-using departments. It is conducive to coordinating the joint scheduling of water diversion from the mainland and water sources on the island, reducing water supply costs, achieving efficient use of water resources, and maximizing the reduction of the contradiction between supply and demand, thereby maintaining the stability of social development. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a flow chart of the implementation steps of the present invention;

[0041] Figure 2 It is a flowchart of the implementation steps of constructing the multi-dimensional joint distribution of runoff in the continental and island regions based on the Copula function in the present invention;

[0042] Figure 3 It is a flowchart of the implementation steps of establishing a joint optimization scheduling model for complex water engineering projects in island areas and optimizing the allocation of water resources under different flood and drought scenarios in the present invention. DETAILED DESCRIPTION

[0043] The present invention is further explained below in conjunction with specific implementation cases.

[0044] A method for optimizing the allocation of water resources across river basins in an island region considering flood and drought conditions, comprising the following steps:

[0045] S1. Collect and organize the hydrological and hydraulic engineering characteristic data of the mainland and island regions, and systematically generalize them according to the geographical location and hydraulic connection of reservoirs in the mainland and island regions;

[0046] S2. Based on the system generalization results, the Copula function is used to construct the multidimensional joint distribution of runoff between the mainland and island regions;

[0047] S3. Based on the multidimensional joint distribution, the probability of wet and dry seasons in the continental and island regions is derived, and the runoff sequences in the continental and island regions under different wet and dry seasons are simulated;

[0048] S4. Establish a joint optimization scheduling model for complex water engineering projects in island areas, use the runoff sequences under different flood and drought conditions as input, and carry out cross-basin water resource optimization allocation in island areas taking into account flood and drought conditions.

[0049] The hydrological characteristic data in step S1 include runoff in the mainland and island regions, and the water conservancy project characteristic data include characteristic parameters of water plants, pumping stations, reservoirs, water pipelines, and the water catchment area of ​​reservoirs.

[0050] In S2, a multi-dimensional joint distribution of runoff between the mainland and island regions is constructed based on the Copula function. Water from the mainland is used as a water supply source, and the island region is divided into two receiving areas according to the location of the water plant. Therefore, the total dimension is three-dimensional.

[0051] like Figure 2 As shown, in S2, based on the system generalization results, the Copula function is used to construct the multidimensional joint distribution of runoff in the continental and island regions, including the following steps:

[0052] S21. Based on the results of system generalization, the Kendall correlation analysis method was used to determine the correlation between runoff in the mainland and island regions;

[0053] S22. Use known marginal distribution models to fit the marginal distribution of runoff in the mainland and island regions, and select the optimal marginal distribution based on the AIC criterion, BIC criterion, RMSE and hypothesis test. The marginal distribution model uses univariate empirical frequency distribution, P-III distribution, Normal distribution, EXP distribution and GEV distribution, and the functions are expressed as follows:

[0054] The univariate empirical frequency distribution is as follows:

[0055] F(x)=P(x≤x m )=(m-0.44) / (n+0.12) (1)

[0056] Where: P is x≤x m The probability of m is x after the samples are sorted from small to large. m The serial number of ; n is the total number of samples x.

[0057] The probability density function of the P-III distribution is:

[0058]

[0059] Where: Γ(α) is the gamma function; α, β, a0 correspond to the shape, scale, and location parameters of the Pearson III distribution, and α>0, β>0, where C s is the skewness coefficient, C v is the coefficient of dispersion, is the sample mean.

[0060] The probability density function of Normal distribution is:

[0061]

[0062] Where: σ is the mean square error, which reflects the degree of discreteness of the sequence. If σ is larger, the corresponding density curve is closer to the x-axis as a whole; μ is the location parameter.

[0063] The probability density function of EXP distribution is:

[0064] f(x)=βe -β(x-μ) (4)

[0065] Where: β>0 is the scale parameter representing the degree of discreteness, and μ is the location parameter.

[0066] The probability density function of the GEV distribution is:

[0067]

[0068] Where: k is the shape parameter, σ is the scale parameter, μ is the location parameter, Z = (x-μ) / σ, where k = 0 is an extreme value type I distribution, k < 0 is an extreme value type II distribution, and k > 0 is an extreme value type III distribution.

[0069] When a marginal distribution satisfies the minimum AIC, BIC and RMSE values ​​and the maximum confidence level p of the hypothesis test, the distribution is regarded as the optimal marginal distribution. The RMSE, AIC and BIC test formulas are as follows:

[0070]

[0071] Where: N is the sample size, P(i) is the theoretical frequency, P m (i) is the empirical frequency, i is the sequence number, and MSE is the mean square error.

[0072] AIC=n ln(MSE)+2k (7)

[0073] Where n is the sample size, k is the number of model parameters, and MSE is the mean square error.

[0074] BIC=ln(n)k-2 ln(L) (8)

[0075] Where: k is the number of model parameters, n is the number of samples, and L is the likelihood function.

[0076] S23. Based on the preferred marginal distribution, the Copula function model is used to fit the multidimensional joint distribution of runoff in the continental and island regions, and the optimal distribution is selected according to the AIC criterion, BIC criterion and RMSE.

[0077] Gumbel Copula, Clayton Copula and Frank Copula are selected to fit the multidimensional joint distribution of runoff in continental and island regions, and each function is expressed as follows.

[0078] Gumbel Copula:

[0079]

[0080] Clayton Copula:

[0081]

[0082] Frank Copula:

[0083]

[0084] Where: u, v, w are marginal distribution functions, u = F(x1), v = F(x2), w = F(x3); θ1, θ2 are the parameters of the Copula function.

[0085] The S3 derives the probability of encountering flood and drought in the continental and island regions based on multidimensional joint distribution, and simulates the runoff sequences in the continental and island regions under different flood and drought conditions. The specific steps are as follows:

[0086] S31. Based on mathematical statistics, a calculation model for the probability of encountering floods and droughts between the continental and island regions is derived.

[0087] The frequency corresponding to the wet and dry level classification in my country is P f =37.5% and P k =62.5%, let P f The amount of water corresponding to the frequency is X pf and P k The amount of water corresponding to the frequency is X pk , then X i ≥X pf For Fengshui and X i ≤X pk For low water, X pk <X i <X pf For flat water, X i is the water inflow in the i-th year. Assume that the water inflow of the three reservoirs is X, Y, and Z, and their marginal functions are u, v, and w, respectively. Then P = (X < x, Y < y, Z < z) = F (u, v, w) = C (u, v, w), and P = (X > x) = 1-P (X < x), then it can be deduced that:

[0088] (1) The probability of abundant X, abundant Y, and abundant Z is:

[0089]

[0090] (2) The probability of X being average, Y being abundant, and Z being abundant is:

[0091]

[0092] (3) The probability of X being dry, Y being abundant, and Z being abundant is:

[0093]

[0094] (4) The probability of X being abundant, Y being abundant, and Z being average is:

[0095]

[0096] (5) The probability of X being flat, Y being abundant, and Z being flat is:

[0097]

[0098] (6) The probability of X being dry, Y being abundant, and Z being average is:

[0099]

[0100] (7) The probability of X being abundant, Y being abundant, and Z being dry is:

[0101]

[0102] (8) The probability of X being normal, Y being abundant, and Z being dry is:

[0103]

[0104] (9) The probability of X withering, Y being abundant, and Z withering is:

[0105] P(X≤X pk , Y ≥ Y pf , Z≤Z pk )=C(u pk , w pk )-C(u pk , v pf , w pk ) (20)

[0106] (10) The probability of X being abundant, Y being average, and Z being abundant is:

[0107]

[0108] (11) The probability of X being flat, Y being flat, and Z being abundant is:

[0109]

[0110] (12) The probability of X being dry, Y being average, and Z being abundant is:

[0111]

[0112] (13) The probability of X being abundant, Y being average, and Z being average is:

[0113]

[0114] (14) The probability of X being equal, Y being equal, and Z being equal is:

[0115]

[0116] (15) The probability of X being dry, Y being flat, and Z being flat is:

[0117]

[0118] (16) The probability of X being abundant, Y being average, and Z being dry is:

[0119] (17) The probability of X being flat, Y being flat, and Z being dry is:

[0120]

[0121] (18) The probability of X withering, Y being flat, and Z withering is:

[0122]

[0123] (19) The probability of X being abundant, Y being dry, and Z being abundant is:

[0124]

[0125] (20) The probability of X being normal, Y being dry, and Z being abundant is:

[0126]

[0127] (21) The probability of X withering, Y withering, and Z withering is:

[0128] P(X≤X pk , Y≤Y pk , Z ≥ Z pf )=C(u pk , v pk )-C(u pk , v pk , w pf ) (32)

[0129] (22) The probability of X being abundant, Y being dry, and Z being average is:

[0130]

[0131] (23) The probability of X being flat, Y being dry, and Z being flat is:

[0132]

[0133] (24) The probability of X withering, Y withering, and Z being flat is:

[0134]

[0135] (25) The probability of X being abundant, Y being dry, and Z being dry is:

[0136] P(X≥X pf , Y≤Y pk , Z≤Z pk )=C(v pk , w pk )-C(u pf , v pk , w pk ) (36)

[0137] (26) The probability of X being flat, Y being dry, and Z being dry is:

[0138] P(X pk <X<X pf , Y≤Y pk , Z≤Z pk )=C(u pf , v pk , w pk )-C(u pk , v pk , w pk ) (37)

[0139] (27) The probability of X withering, Y withering, and Z withering is:

[0140] P(X≤X pk , Y≤Y pk , Z≤Z pk )=C(u pk , v pk , w pk ) (38)

[0141] S32. Based on the marginal distribution and multidimensional joint distribution obtained in S2 and the probability calculation model of encountering flood and drought in the mainland and island areas, calculate various probability values ​​of encountering flood and drought, and analyze the encountering flood and drought situations in the mainland and island areas, including the situations where the runoff in the mainland and island areas is synchronous with flood and drought and asynchronous with flood and drought.

[0142] Based on the probability values ​​of encountering flood and drought, the possibility of synchronous flood and drought or asynchronous flood and drought in runoff between mainland and island areas is assessed, among which the focus is on the situation where the runoff between mainland and island areas occurs simultaneously.

[0143] S33. Simulate runoff sequences in continental and island regions under different flood and drought conditions.

[0144] Based on the marginal distribution, the runoff corresponding to different probabilities of flood and dry seasons is found, and the runoff closest to it is found in the actual runoff. The original runoff sequence is subjected to the proportional relationship between the two using the same multiple ratio method to generate the annual monthly runoff sequence under different encounter situations.

[0145] like Figure 3 As shown, the S4 establishes and solves the joint optimization scheduling model of complex water engineering groups in island areas to optimize the allocation of water resources under different flood and drought scenarios, including the following steps:

[0146] S41. Establish a joint optimization dispatching model for complex water projects in island areas, and use the runoff sequence under different flood and drought conditions as input to solve the optimization dispatching model and obtain the corresponding set of optimization configuration schemes. The specific steps are as follows:

[0147] S411. Determine the objective function of the optimization configuration model, including: maximizing the water supply guarantee rate, maximizing the water supply economic benefit, and minimizing the water supply cost.

[0148] (1) Goal 1: Maximum water supply guarantee rate

[0149]

[0150] In the formula, x ij is the total water supply from water source i to water user j, m 3 ; I is the number of water sources, J is the number of water users; WD j is the total amount of water required by water user j during the scheduling period, m 3 .

[0151] (2) Goal 2: Maximize economic benefits of water supply

[0152]

[0153] Where: α i is the water supply order of water source i, β j is the fairness coefficient of the water user, x ij is the amount of water supplied from water supply source i to water receiving user j, b ij The unit water economic benefit coefficient of water supplied by water source i to water user j.

[0154] (3) Goal 3: Minimize water supply costs

[0155] The water sources of island cities include local water and mainland water. The cost of unit water intake varies due to different water supply methods and distances. In order to better optimize the water supply structure and fully improve the utilization efficiency of local water, it is necessary to calculate the cost in detail and accurately to achieve improved economic benefits.

[0156] min f3(x)=C total =C island +C mainland (41)

[0157] Where: C total Total cost of water supply, RMB; C island Cost of supplying water to the island, RMB; C mainland The cost of diverting water to the mainland is RMB.

[0158] S412. Determine the constraints of the optimization configuration model, including: water balance constraints, reservoir water supply constraints, pump station flow capacity constraints, pipeline water transmission capacity constraints, island water supply and mainland water diversion constraints, user water demand constraints, and variable non-negative constraints.

[0159] (1) Water balance constraints

[0160] All water supply facilities and water receiving facilities must meet the water balance constraints. Among them, the water balance formula of the water storage project (reservoir) is:

[0161] S t+1 =S t +I t -ET t -ST t -WS t (42)

[0162] Where: S t , S t+1 are the initial and final water storage of the reservoir in the current period, m 3 ;I t , WS t is the inflow and outflow of the reservoir in the current period, m 3 ET t , ST t are the evaporation and leakage in the current period, which are considered to be small and can be ignored in this study, m 3 .

[0163] Water balance formula at water diversion point:

[0164]

[0165] Where: is the total inflow of node x in the current period, m 3 ; is the total outflow of node x in the current period, m 3 .

[0166] (2) Constraints on reservoir water availability

[0167] There are constraints on the water supply of reservoirs and water plants. In order to meet the needs of beneficial scheduling and flood control scheduling, the operating water level of the reservoir is usually limited to a certain range. There is an upper limit on the amount of water that the water plant can process per day, the maximum water delivery capacity of the water pipeline, and the water supply of the mainland water diversion project. The above factors constitute the constraints on the water supply when optimizing the allocation of water resources.

[0168]

[0169] Where: WS i is the water supply of water source i in the current period, m 3, which is calculated based on the current reservoir capacity and the inflow flow in the current period and the water supply (outflow flow) to each water plant in the previous period. The water supply constraint means that the total water supply of a reservoir to each water plant does not exceed the water supply capacity of the reservoir in the current period.

[0170] (3) Pump station flow capacity constraints

[0171]

[0172] Where: m is the amount of water supplied from water source i to user j through pumping station, 3 , is the amount of water supplied by water source i to water user j by gravity, siphon, etc., m 3 ; is the maximum pumping flow rate that can be achieved by equipment No. n in the pumping station within a unit period during the dispatching process, m 3 .

[0173] (4) Pipeline water delivery capacity constraints

[0174]

[0175] Where: is the maximum flow capacity of pipeline m in a unit period during the dispatch process, m 3 .

[0176] (5) Constraints on water supply to the island and water diversion from the mainland

[0177] The upper limit of the total water withdrawal within one year and the upper limit of the total water diversion from the mainland are determined based on the local government's planning for the development and utilization of water resources and the upper limit capacity of water diversion projects.

[0178] X island ≤W island_max (47)

[0179] X mainland ≤W mainland_max (48)

[0180] Where: X island is the total amount of water taken from the island in 12 months of the year, m 3 ;X mainland is the total amount of water diverted from the mainland in one year, m 3 ; W island_max The upper limit of water withdrawal from the island in one year, m 3 ; W mainland_max is the upper limit of water diversion from the mainland within one year, m 3 .

[0181] (6) User water demand constraints

[0182] The water supply volume shall not exceed the water demand range of each water user. When the water supply volume is lower than the user's water demand, normal economic and social activities such as production and life cannot be carried out normally, and the ecological governance task is hindered, resulting in a series of social problems such as obstruction of economic and social development and degradation of the human living environment. When the water supply volume exceeds the user's water demand, it causes waste of water resources and increases the water treatment costs of relevant water users. Therefore, a reasonable water demand constraint needs to be set.

[0183] WD j ≥α j (49)

[0184] Where: WD j is the total amount of water required by water user j during the scheduling period, m 3 ; α j is the lower limit of the total water volume required by the water users in the scheduling period, m 3 .

[0185] (7) Non-negative constraints on variables

[0186] x ij ≥0 (50)

[0187] Where: x ij is the total water supply from water source i to water user j, m 3 .

[0188] S413. The NSGA-II algorithm is used to solve the model. The runoff sequence under different flood and drought conditions is taken as input to obtain a set of water resource allocation plans under different flood and drought conditions.

[0189] S42, the optimal solution of the multi-attribute decision-making method based on subjective and objective combined weighting, the specific steps are as follows:

[0190] S421. Consider economic, social and ecological benefits to establish an evaluation index system. Decision makers formulate indicators based on economic benefits, social needs and ecological requirements. Indicators refer to the judgment basis that decision makers subjectively give to the evaluation object, or the evaluation criteria that determine the pros and cons of the selected options.

[0191] S422. Determine the subjective weight and objective weight of each indicator. Under different circumstances of abundance and scarcity, the importance of each indicator is different. The subjective weight of each indicator is determined by the analytic hierarchy process, and the objective weight of each indicator is determined by the entropy weight information method.

[0192] S423. Use the additive synthesis method to obtain the combined weight of each indicator as the basis for judging the importance of each indicator, and rank the various plans to obtain the relatively optimal plan.

[0193] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in this field.

[0194] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for optimizing the allocation of water resources across river basins in island areas taking into account the occurrence of floods and droughts, characterized in that: The following steps are involved: S1. Collect and organize the hydrological and hydraulic engineering characteristic data of the mainland and island regions, and systematically generalize them according to the geographical location and hydraulic connection of reservoirs in the mainland and island regions; S2. Based on the system generalization results, the Copula function is used to construct the multidimensional joint distribution of runoff between the mainland and island regions; S3. Based on the multidimensional joint distribution, the probability of wet and dry seasons in the continental and island regions is derived, and the runoff sequences in the continental and island regions under different wet and dry seasons are simulated; S4. Establish a joint optimization dispatching model for complex water projects in island areas, take the runoff sequence under different flood and drought conditions as input, and carry out cross-basin water resources optimization allocation in island areas considering flood and drought conditions; In S2, based on the system generalization results, the Copula function is used to construct the multidimensional joint distribution of runoff in the continental and island regions. The specific steps are as follows: S21. Based on the results of system generalization, determine the correlation between runoff in the mainland and island areas; S22. Use marginal distribution models to fit the marginal distribution of runoff in the mainland and island regions respectively, and select the optimal marginal distribution based on the AIC criterion, BIC criterion, RMSE and hypothesis test; the marginal distribution model uses univariate empirical frequency distribution, Pearson three-type distribution, exponential distribution, generalized extreme value distribution, normal distribution and lognormal distribution; S23, based on the optimal marginal distribution, using known Copula functions to fit the multidimensional joint distribution of runoff in the mainland and island regions respectively, and selecting the optimal distribution according to AIC, BIC and RMSE; the Copula function uses "Gaussian", "Clayton", "Frank", "Gumbel" and "Vine" functions; The specific steps of S3 are as follows: S31. Derive the probability calculation model of wet and dry seasons in mainland and island regions based on mathematical statistics methods; S32, based on the marginal distribution and multidimensional joint distribution obtained in S2 and the probability calculation model of flood and drought encounters in the continental and island regions, calculate various flood and drought encounter probability values, and analyze the flood and drought encounter situations in the continental and island regions, including the situations where the runoff in the continental and island regions is synchronous with flood and drought and asynchronous with flood and drought; S33, simulate runoff sequences in continental and island regions under different flood and drought conditions; Step S4 specifically includes the following steps: S41. Establish a joint optimization dispatching model for complex water projects in island areas, take the runoff sequence under different flood and drought conditions as input, solve the optimization dispatching model to obtain the corresponding set of optimization configuration solutions; S42. Optimal selection of multi-attribute decision-making method based on subjective and objective combined weighting.

2. The method for optimizing the allocation of inter-basin water resources in island areas taking into account the occurrence of floods and droughts as claimed in claim 1, characterized in that: In S2, the number of latitudes n1 in the continental area is determined according to the number of water sources, and the number of latitudes n2 in the island area is determined according to the number of water plants, and the total latitude N = n1 + n2.

3. The method for optimizing the allocation of water resources across river basins in island areas taking into account the occurrence of floods and droughts as claimed in claim 1, characterized in that: The S33 simulates the runoff sequences of the mainland and island areas under different flood and drought conditions. Specifically, based on the marginal distribution, the runoff corresponding to different flood and drought probabilities is found, and the closest runoff is found in the actual runoff. The original runoff sequence is fitted with the runoff sequence under different encounter scenarios by using the same multiple ratio method based on the proportional relationship between the two.

4. The method for optimizing the allocation of water resources across river basins in island areas taking into account the occurrence of floods and droughts as claimed in claim 1, characterized in that: In the above S41, a joint optimization dispatching model for complex water engineering projects in island areas is established. The runoff sequence under different flood and drought conditions is used as input to solve the optimization dispatching model to obtain a corresponding set of optimization configuration schemes. The specific steps are as follows: S411. Determine the objective function of the optimization configuration model, including maximizing the water supply guarantee rate, maximizing the water supply economic benefit, and minimizing the water supply cost, which are: In the formula, x ij is the total water supply from water source i to water user j, in m 3 ; I is the number of water sources; J is the number of water users; WD j is the total amount of water required by water user j during the scheduling period, in m 3 ; α i is the water supply order of water source i; β j is the fairness coefficient of the water user; b ij The unit water economic benefit coefficient of water supply from water source i to water user j; C total is the total cost of water supply, in yuan; C island Cost expenditure for water supply to the island, in yuan; C mainland Cost expenditure incurred for diverting water from the mainland, in yuan; S412. Determine the constraints of the optimization configuration model, including water balance constraints, reservoir water supply constraints, pump station flow capacity constraints, pipeline water delivery capacity constraints, island water supply and mainland water diversion constraints, user water demand constraints and variable non-negative constraints, which are: In the formula, S t , S t+1 are the initial and final water storage of the reservoir in the current period, in m 3 ; I t , WS t The inflow and outflow of the reservoir in the current period, in m 3 ; ET t 、ST t They are the evaporation and leakage in the current period, in m 3 ; The total inflow of node x in the current period, in m 3 ; The total outflow of node x in the current period, in m 3 ; WS i is the water supply of water source i in the current period, in m 3 , which is calculated based on the current reservoir capacity and the inflow flow in the current period and the outflow flow in the previous period; The amount of water supplied from water source i to user j through pumping stations, in m 3 ; The amount of water supplied by water source i to water user j by gravity or siphon, in m 3 ; It is the maximum pumping flow value that can be achieved by equipment No. n in the pump station during the dispatching process in a unit time period, in m 3 ; is the maximum flow capacity of pipeline m in a unit period during the dispatch process, in m 3 ;X island The total amount of water taken from the island in one year, in m 3 ;X mainland is the total amount of water diverted from the mainland in one year, in m 3 ; W island_max The upper limit of water intake on the island within a year, in m 3 ; W ,ainland_max The upper limit of water diversion from the mainland in one year, in m 3 ; WD j is the total amount of water required by water user j during the scheduling period, in m 3 ; α j The lower limit of the total water volume required by water user j during the scheduling period, in m 3 ; x ij is the total water supply from water source i to water user j, in m 3 ; S413. According to the characteristics of the model, a suitable solution method is selected to solve the model, and the runoff sequence under different flood and drought conditions is used as input to obtain a set of water resource allocation plans under different flood and drought conditions; the solution method adopts a non-dominated sorting genetic algorithm (NSGA-II algorithm), a large system decomposition-dynamic programming aggregation algorithm, a linear weighted method or a hierarchical solution method.

5. The method for optimizing the allocation of inter-basin water resources in island areas taking into account the occurrence of floods and droughts as claimed in claim 1, characterized in that: The preferred solution of the multi-attribute decision-making method based on subjective and objective combined weighting in S42 is as follows: S421. Establish an evaluation index system taking into account economic, social and ecological benefits; S422. Determine the subjective weight and objective weight of each indicator; the subjective weighting method adopts the Delphi method or the hierarchical analysis method; the objective weighting method adopts the principal component analysis method, the two-stage method or the entropy weight information method; S423. Use the subjective and objective combined weighting method to obtain the combined weight of each indicator as the basis for judging the importance of each indicator, and perform optimization ranking on each plan to obtain the relatively optimal plan; the subjective and objective combined weighting method adopts the additive synthesis method, the multiplicative synthesis method, the extreme difference maximization combined weighting method or the combined weighting method based on objective correction of subjective.

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